The primary reason for dry turkey is overcooking it. The main reason people over cook it is not having an accurate temperature probe and not knowing the right temperature to pull it. I thought I had a good thermometer early on until I discovered ThermoWorks. Their thermometers are what you will find in a majority of commercial kitchens. There are other details like brining the turkey, cooking temperature, etc. check this article from ThermoWorks as a start: https://www.thermoworks.com/cooking-turkey/